In general, conventional speaker has been used, as shown in FIG. 6, a trumpet-shaped frame having permanent magnet to the backward is installed and on the whole surface of the inner side of the frame, a vibration plate is installed to change the electrical signal to voice signal by its vibration, and onto the frame, speaker is composed by forming a large number of the through hole so that the voice frequency radiated to the backward among the radiated voice frequency by the vibration of the vibration plate, can be smoothly radiated to the backward and the speaker composed as the above is fixedly installed to the inside of the case.
Conventional speaker composed as the above, the voice frequency generated from the vibration plate according to the vibration of the vibration plate is radiated to the foreward and backward of the vibration plate, then the voice frequency radiated to the foreward of the vibration plate is radiated to the foreward through the exhaust radiating hole composed to the foreward of the speaker case and then the user can listen it, but the voice frequency radiated to the backward of the vibration plate is radiated to the backward of the speaker through the through hole of the frame formed to the backward of the vibration plate.
The voice frequency radiated to the backward is reflected by the wall surface of the case inner side and it spreads out again to the new direction according to the direction of the wall surface and a part of the voice frequency is diminished by reflecting to the another wall surface, so there was a problem such as generating the noise as there exists new vibration by mixing the rest of the voice frequency reflecting continuously to the new voice frequency coming out to the backward of the vibration plate.